Study members were first asked about their children in [[questionnaires:1966|1966]] (at age 20 years). Since then the birth of each child to a study member has been recorded throughout their adult life including date of birth and sex of the child.
They were also asked about the fertility of their parents, in terms of the number of children in the household and their own rank (birth order amongst siblings) in the family. \\ \\ Derived variables include the number of children born to each study member and the age of the study member at the time of each birth. These were first created up to [[questionnaires:1982|1982]], and then updated at [[questionnaires:1989|1989]], [[questionnaires:1999|1999]] and [[questionnaires:2009|2006-10]]. The age at the birth of their last child has also been derived. As very few women have had children since the age of 43 years an additional variable was derived which imputed for missing values the total number of children born by [[questionnaires:1999|1999]] to be the figure from [[questionnaires:1989|1989]]. This imputation was only undertaken for women.
In [[questionnaires:1989|1989]], [[questionnaires:1999|1999]] and [[questionnaires:2009|2006-10]] study members were asked whether they had had any grandchildren, but the date of birth was only recorded for the first grandchild.
In [[questionnaires:2015|2014-16]], study members were also asked whether they had any grandchildren, but the questions were more focused on caring for grandchildren or for visiting grandchildren.